How to build and install a Python application is dependent on the OS which is being used to package it. Typically, each operating system only allows the application to be built for the same platform, meaning only Windows can create Windows .exe files, and so on. Pip, however, is able to run on all platforms, so can be used as a way of packaging once for any system.
For a user who will already have Python installed, we can distribute our applications as pip packages. This will work on all platforms, but requires the user to have the correct version of Python and pip already installed, and also to be able to use the command line.